The present invention relates to surface scanning of parts and more particularly concerns improved scanning methods and apparatus to provide precision information concerning surface characteristics, configuration, orientation and discontinuities.
Electro-optical parts inspection and identification broadly involves the collection and analysis of light reflected from the surface of an object being monitored. In general, prior scanning apparatus, such as the video camera, for example, involve the equivalent of a point source of scanning. Light is transmitted to and received from the part at varying angles for different points of the object being scanned. Such arrangements require fixed positioning and orientation of the part being scanned so that the part is usually mounted in a fixture that predetermines position and orientation with respect to the scanning device. A point scanning source, such as that providing a conical scan, for example, has an illuminating beam that strikes different portions of the scanned surface at different angles. Surface elevation characteristics, such as cavities or protuberances, will reflect differently in different orientations and different angles of illumination so that reflection intensities afford less useful information.
For optimum precision in identification and measurement of surface detail, for improved repeatability of measurement, and for greater freedom from orientation and position restraint, all points on the surface of the part should be illuminated by light beams that are at all times parallel to one another, or always normal to a selected plane through the part. For example, such an orthogonally directed scan is required for measurement of part dimensions in a plane normal to the beam and for measuring surface elevation features in directions parallel to the beam. With such a perpendicular pattern of parallel scanning beams there is available a considerably greater flexibility in part position and orientation relative to the scanner, and reflections from surface areas of unique roughness configurations will have greater uniformity and repeatability. The lack of orthogonal scanning imposes substantial limitations on usefulness of the scanning.
In those prior art scanning devices employing a projected scanning beam and a receiver for collecting light reflected from the object, the receiver must be large enough to receive light reflected from all areas of the object that are illuminated during the entire scan. In such arrangements the size of the part that can be scanned is relatively small, being limited by practical and economic considerations that limit the size of a light receiver, such as an optical lens, a collecting mirror or an array of detectors or optical fibers.
Accordingly, it is an object of the present invention to provide scanning apparatus and methods that avoid or minimize above-mentioned problems.